This invention relates to a bat used in baseball, and more particularly it relates to a bat made of fiber reinforced resin and a method of producing such a bat.
There is already known a bat used in baseball including soft ball made of fiber reinforced resin. Such a bat is produced usually by placing cloth, roving or braid of continuous fibers impregnated with a thermosetting resin in a mold cavity in the form of bat, and then pressing and heating the resin to cure. There is also known a bat which is produced by injection molding of fiber reinforced thermoplastic resin as described in, for instance, Japanese Utility Model Application Laid-open No. 54-134565 and Japanese Patent Publication No. 59-10228.
The conventional bat of fiber reinforced resin as above mentioned uses an epoxy resin or a polyester resin reinforced with continuous fibers, and such a resin provides a solid and light bat. However, the production needs complicated and laborious steps. For instance, it is complicated and laborious to prepare prepregs and laminate the prepregs to form a preformed material. The conventional molding of such a preformed material needs a molding cycle as long as about 20-40 minutes at temperatures of about 100.degree.-150.degree. C. Thus, the conventional method needs a large number of molds for mass production, and hence the resultant bats are costly.
The conventional bats have further defects that they are rather brittle on account of properties which the resin as above mentioned originally has, although they are hard, and in addition they are of rather small vibration damping rate and wear resistance. Moreover, molded materials as molded have many voids on the surface and in the inside to necessitates complicated after treatment. As the case may be, there is obtained a bat having a smaller strength than expected.
On the other hand, there is also known a hollow bat which is produced by injection molding of a thermoplastic resin reinforced with short fibers. However, such a bat is inferior in strength and rigidity to a bat of a thermosetting resin reinforced with continuous fibers. Thus, such a hollow bat needs a reinforced outer layer of a large thickness, or reinforcing ribs in the hollow. This reduces freedom of design remarkably and prevents the production of light bats. Further, the injection molding needs a high molding pressure, and hence needs molds which bear such a high molding pressure, so that the production cost is high.
It is an object of the invention to provide a baseball bat formed of fiber reinforced resin and having a high strength and rigidity.
It is also an object of the invention to provide a method of producing such a bat in a high productivity.